Generally, rubber compositions used in manufacture of rubber articles such as tires, conveyor belts, anti-vibration rubbers and seismic isolation rubbers are required to have high durability. Here, conventional diene based rubbers used in the rubber industry frequently, such as butadiene rubbers (BR) and styrene-butadiene rubbers (SBR), have excellent wear resistance, etc., but do not have sufficient resistance against cracks due to ozone, time degradation, etc., i.e., crack growth resistance. Then, in order to satisfy the aforementioned requirement, various rubber components and rubber compositions have been developed.
For example, PTL1 discloses a copolymer of a conjugated diene compound and a non-conjugated olefin in which conjugated diene parts (parts derived from a conjugated diene compound) have a cis-1,4 bond content of greater than 70.5 mol % and a non-conjugated olefin is contained in an amount of 10 mol % or more, and discloses that this copolymer is used for manufacturing rubber having good properties, such as crack growth resistance.